An active matrix type liquid crystal display apparatus producing a multi-gradation display is known in the prior art. This multi-gradation display is performed by selecting one reference voltage corresponding to the gradation display data from among as many reference voltages as display gradations using an analog switch and driving the liquid display apparatus at the selected reference voltage.
FIG. 1 is a block diagram showing a conventional liquid crystal drive apparatus for driving an active matrix type liquid crystal display apparatus. This liquid crystal drive apparatus is provided with first latch 1, second latch 2 and decoder 3 for every vertical pixel line of the liquid crystal display apparatus.
First latch 1 reads 3-bit gradation data D0 to D2 that specify 8 gradations for each vertical pixel line during one horizontal scanning period. That is, this gradation data D0 to D2 are latched by first latch 1 and held for only one horizontal scanning period.
Second latch 2 supplies gradation data D0 to D2 held in first latch 1 to decoder 3 in next one horizontal scanning period. Decoder 3 decodes gradation data D0 to D2 from second latch 2 and outputs decoded signals S0 to S7 to control terminals of analog switches A0 to A7 respectively.
These analog switches A0 to A7 selectively output reference voltages V0 to V7 supplied to the input terminal in association with decoded signals S0 to S7. That is, one of reference voltages V0 to V7 is selected by decoded signals S0 to S7 and output as a liquid crystal drive voltage.
Reference voltages V0 to V7 correspond to gradation levels as shown in FIG. 2. Therefore, a reference voltage is selected based on the gradation data, the reference voltage is output to the liquid crystal panel as a voltage to be applied, and in this way the amount of transmitted light corresponding to the applied voltage is obtained allowing a gradation display.
However, the conventional liquid crystal drive apparatus is not sufficient to drive liquid crystals at high speed. In line with widespread use of the Internet there is a growing demand for high-speed transmission of large-volume data such as images in recent years and multi-gradations are also required to be implemented. Displaying moving pictures in particular requires high-speed drive and a multi-gradation display of liquid crystals.